It has been known from long ago that an isocyanate and a hydroxy compound can be obtained by the pyrolysis of an N-substituted carbamic acid ester. The basic reaction thereof is represented by the following formulae (a) and (b):R(NHCOOR′)n→R(NCO)n+nR′OH  (a)(R′NHCOO)nR→nR′NCO+R(OH)n  (b)wherein
R represents an n-valent organic residue, R′ represents a monovalent organic residue, and n represents an integer of 1 or greater.
Various studies have been conducted so far, regarding a method for producing an N-substituted carbamic acid ester that is used as a raw material.
For example, Patent Document 1 describes a method comprising reacting a primary diamine and alcohol with urea or a carbonic acid derivative in the presence of a catalyst to convert them to an N-substituted carbamic acid ester. In addition, Patent Document 2 describes a method comprising producing bisurea from an aliphatic primary polyamine, urea and alcohol, and then producing an N-substituted carbamic acid ester from the bisurea. Moreover, Patent Document 3 describes a method comprising partially reacting urea with alcohol in a first step and then supplying a diamine to the reaction product in a second step to produce an N-substituted carbamic acid ester.